Patent GB-1012025-A (GB)
Title: An inverter for producing an alternating current in a load from a direct current power supply
IPC: H02M7/515
Filed: 1962-05-04
Abstract: 1,012,025. Converting. GENERAL ELECTRIC CO. May 4, 1962 [May 8, 1961], No. 17297/62. Heading H2F. [Also in Division G3] An inverter (as shown in Fig. 1, a parallel inverter) comprising silicon controlled rectifiers 15, 16 provided with reversely connected diodes 19, 22 for use with reactive loads, is provided with circuitry (7) to provide pulses to fire the rectifiers and circuitry (8) to provide pulses to shut these off independently of the load. The circuit 7 and 8 are both supplied from an A.C. generator 68, the circuit 7 comprising a phase-shifting combination 87, 88 connected with a saturable reactor 77 and transformer 78 to supply pulses to the rectifier gates from secondary windings 80, 81, via diodes 82, 83. The circuit 8 comprises a saturable transformer 71 supplying a transformer 53, so that pulses are derived in the secondary winding 54 (which lies in the main circuit of the rectifiers) to provide reverse voltages to shut these off. In operation with rectifier 15 conducting the anode of this rectifier is held at the potential of the negative pole of the supply battery 14 by the presence of the uncharged capacitor 49. A commutating pulse derived in the upper half of winding 54 raises the cathode potential of rectifier 15 sufficiently to shut this off. Some short time later a pulse from winding 81 fires the rectifier 16, and the process is continued with the rectifier 15, 16 firing alternately. The reverse diodes 19, 22 across the rectifiers 15, 16 permit currents to flow under reactive load conditions. In alternative embodiments (Figs. 3, 4 and 5, not shown) parallel inverters with modified shut-off circuits are disclosed. In Fig. 3 a reverse-pulse transformer in a common cathode connection of the rectifiers is used. In Fig. 4 capacitors 49, 50 are dispensed with, and diodes 19, 22 are connected to tappings on the main transformer winding. A series circuit of saturable transformer and capacitor is disposed across each rectifier so that a commutating pulse to the transformer charges the capacitor which then discharges to shut off the rectifier. In Fig. 5 a capacitor 42 is charged by a commutating pulse until a saturable reactor 43 saturates when the capacitor discharges through this reactor and a cathode inductor 44 inducing in the latter a reverse voltage to shut off the rectifier 15. Fig. 6 (not shown) discloses a series inverter with centre-tapped supply. An automatically regulated three-phase bridge inverter is disclosed in Fig. 7. Firing pulses are derived from circuits 7 and commutating pulses are applied to commutating transformers 52, from a source 134 via a circuit 122 comprising rectifier 130, capacitor 128 and resistors 127, 129. A measure of the output current is determined by current transformer 102, rectified by bridge 112 and added to the main supply 14 applied to the circuit 122. The value of this voltage determines the time at which capacitor 128 is charged sufficiently for rectifier 130 to conduct (a firing pulse synchronized with the supply being applied from circuit 134) and apply a commutation signal to the transformer 52.